The present invention relates to an emitter for emitting electromagnetic pulses, to a system for testing fiber-optic components and to a method of testing them.
Said emitter, of the type comprising:
a generator for generating at least one electromagnetic pulse, especially a light pulse; and
at least one optical fiber capable of transmitting an electromagnetic pulse generated by said generator for the purpose of injecting it,
is able to be applied more particularly, although not exclusively, to a test system for determining characteristic parameters, especially the losses, of a fiber-optic component, in particular a fiber-based component, a fiber-based link or a fiber-optic network.
U.S. Pat. No. 5,251,002 discloses such a test system, which comprises:
such an optical emitter or source capable of emitting a light pulse;
a photoreceiver capable of measuring optical characteristics of a light pulse emitted by said optical source and transmitted by a fiber-optic component; and
data acquisition, storage and processing means which receive the measurements generated by said photoreceiver for said fiber-optic component to be tested and for a reference fiber-optic component and which determine, on the basis of these measurements, the losses of said fiber-optic component to be tested.
In a known manner, said optical source or said emitter has emission conditions, especially with regard to the emission solid angle and the illumination surface, which are fixed and uniform.
In addition, said known test system allows tests to be carried out only for a defined configuration of the light beam used, as emitted by said optical source. This known test system therefore uses a method which measures only the losses relative to a single defined pulse emitted by said optical source.
However, in practice, the configuration of the light beam generated by the optical source is not always that actually used in said optical component to be tested. Consequently, the reliability of this test system is unsatisfactory.
To increase the reliability, it is necessary to suitably sample the aforementioned illumination or emission conditions, which may vary from 0% to 100% of the area of the core in the case of the emission surface, and from 0% to 100% of the numerical aperture, in the case of the emission solid angle. In the situations usually encountered, the conditions may vary from 70% to 100%.
For this purpose, it is advised to provide a sampling increment of at most 2%. This therefore assumes that at least some fifteen different optical sources are used, each of which has appropriate illumination conditions, in order to obtain satisfactory sampling.
This solution is therefore hardly satisfactory, especially because of the high cost, the lengthy implementation time and the considerable amount of handling.
It is an object of the present invention to remedy these drawbacks, and especially those associated with the existence of fixed and uniform emission conditions of the optical source.
It relates to an emitter for emitting electromagnetic pulses, which is capable of emitting electromagnetic pulses having emission geometry characteristics (emission solid angle and emission area) which are variable.
For this purpose, according to the invention, said emitter for emitting electromagnetic pulses, comprising:
a generator for generating at least one electromagnetic pulse; and
at least one optical fiber capable of transmitting an electromagnetic pulse generated by said generator for the purpose of emitting it,
is noteworthy in that it includes in addition at least one optical cavity:
which is placed in the path of an incident electromagnetic pulse transmitted by said optical fiber; and
which has an input provided with a first partially reflecting mirror and an output provided with a second partially reflecting mirror, said first and second mirrors being arranged so as to create at the output of said optical cavity, from a single incident electromagnetic pulse, a train of emitted electromagnetic pulses which have variable geometry characteristics and are associated with said incident electromagnetic pulse.
Thus, by virtue of said optical cavity, the emitted pulse train comprises pulses subjected to variable numbers of reflections off said mirrors and therefore traveling variable distances in said cavity. However, since the aforementioned geometry characteristics vary, in a known manner, according to the distance traveled, the various pulses of said pulse train have variable geometry characteristics (emission solid angle and emission area).
Consequently, by choosing appropriate characteristics of said optical cavity, and especially the reflection/transmission ratio of the partially reflecting mirrors and the distance between them, a plurality of pulses having predetermined emission characteristics can be formed.
In particular, when said emitter is applied to a test system of the aforementioned type, it is possible to form a particular pulse train comprising the various possible configurations of the light beams likely to be transmitted by the component to be tested.
This enables the aforementioned drawbacks of the known test system, described in particular in U.S. Pat. No. 5,251,002, to be remedied since it is no longer necessary to provide a plurality of different optical sources in order to carry out an overall test.
Moreover, advantageously, at least one of said first and second mirrors is linked to two lengths of the optical fiber:
in a first embodiment, directly by opposed faces; and
in a second embodiment, via an associated optical coupling means.
In this second embodiment, said or each of said optical coupling means advantageously comprises:
in a first embodiment, two lenses optically linking said two lengths of the optical fiber, the mirror associated with said optical coupling means being placed between said lenses;
in a second embodiment, a single half-wave graded-index lens, said mirror being placed on that face of said optical coupling means which is internal to said optical cavity; and
in a third embodiment, two quarter-wave graded-index lenses optically linking said two lengths of the optical fiber, the mirror associated with said optical coupling means being placed between said lenses.
Moreover, the emitter according to the invention advantageously comprises means preventing a pulse generated by said generator from returning toward the latter. For this purpose, said means preferably include at least one light trap which cooperates with the optical coupling means associated with said first mirror.
Furthermore, said generator is advantageously capable of generating at least two pulses, of different wavelengths, thereby making it possible in particular, when applying it to a test system, to measure simultaneously the losses at several operating wavelengths of certain types of links such as, for example, video communication links operating at wavelengths of 0.85 xcexcm and 1.3 xcexcm.
The present invention also relates to a test system of the aforementioned type.
According to the invention, said test system is noteworthy in that the optical source of this system comprises a light-pulse emitter, as mentioned above.
In addition to the advantages indicated above, this test system according to the invention has an operating life (or lifetime) longer than that described in U.S. Pat. No. 5,251,002. This is because this known latter system, which includes electrooptic switches, only allows a relatively small number of uses and, in addition, it is sensitive to the environmental conditions, something which is not the case in the system according to the invention, which has no mechanical moving parts.
It should also be noted that the optical fiber of the pulse emitter generally has characteristics (core diameter and numerical aperture) identical to those of the fiber-optic component to be tested. This makes it possible to vary over time, in the same direction, the emission area and the emission solid angle, these latter two geometry characteristics decreasing for each successive pulse.
However, in one particular embodiment, the electromagnetic pulse emitter is formed in such a way that one of said geometry characteristics is constant and the other varies.
For this purpose, according to the invention:
in order to obtain a constant emission solid angle, an optical fiber is provided which has the same core diameter as the core diameter of the fiber-optic component to be tested, but with a larger numerical aperture; and
in order to obtain a constant emission area, an optical fiber is provided which has the same numerical aperture, but a larger core diameter than the component to be tested.
Moreover, the present invention also relates to a test method for determining the value of at least one characteristic parameter, such as the attenuation of the electromagnetic intensity, of a fiber-optic component, which method makes it possible in particular to remedy the aforementioned drawbacks of the known method implemented by the test system described in U.S. Pat. No. 5,251,002.
This known method, as indicated above, takes measurements for only a single type of pulse. Thus, when information is needed for a plurality of different pulses, it is necessary to use said known method for each of said pulses. In addition, to be able to adapt or compare the results then obtained, it is necessary to create the same operating conditions for each of these different tests. This is time-consuming, tedious and a source or errors.
In order to remedy these drawbacks, said method according to the invention for determining the value of at least one characteristic parameter of a fiber-optic component, in which method:
a) at least one electromagnetic pulse is generated, which is injected into said fiber-optic component;
b) measurements relating to said electromagnetic pulse transmitted by said fiber-optic component are carried out; and
c) said characteristic parameter is determined at least from said measurements,
is noteworthy in that, in step a), an electromagnetic pulse train is generated, at least some of the electromagnetic pulses of which have different values for at least one optical characteristic, especially an emission geometry characteristic such as the emission area or the emission solid angle, and in that, in step c), the value of said characteristic parameter is determined for each of said different electromagnetic pulses of said pulse train.
Thus, thanks to the invention, tests for a plurality of different pulses are carried out in a single implementation of the method. This has a number of advantages, and especially a reduction in the length and the cost of the tests when these have to be carried out for a plurality of different pulses, and an increase in the accuracy, since it is no longer necessary to try to recreate identical operating conditions for a plurality of different tests.
Advantageously, in order to generate said pulse train:
a plurality of pulses is formed from one incident electromagnetic pulse; and
said pulses are made to travel different distances in at least one optical fiber, said pulses forming said pulse train at the exit of said optical fiber.
This is preferably carried out using the aforementioned emitter and in accordance with the invention.
In addition, said characteristic parameter advantageously represents the losses of said fiber-optic component and, in step b), measurements are carried out on said fiber-optic component and on a reference fiber-optic component.